Vehicle drive trains known from the prior art are typically designed having an internal combustion engine and at least one transmission device, disposed between the internal combustion engine and an output drive, by means of which the transmission ratios that are required depending on the operating state can be provided.
Such transmission devices known per se and implemented as automatic transmissions, are designed having shift elements for implementing different transmission ratios, by means of which a present torque can be transferred in a frictionally-engaging manner. With a request for implementing a defined transmission ratio, at least one or a plurality of the frictionally engaging shift elements are disengaged from the power flow of a transmission device, while at least one or more additional frictionally engaging shift elements are engaged into the power flow of a transmission device to implement the required transmission ratio. During the process of engaging a frictionally engaging shift element, no particular synchronization measures are necessary for guaranteeing desired shifting comfort and shifting without any tractive force interruption, because sought-after shifting comfort and also shifting without any tractive force interruption can be achieved by means of frictionally engaging shift elements at defined contact pressures within a wide range of rotational speed differences.
Since, in a manner known per se, such transmission devices can only be operated with insufficient degrees of efficiency because of drag losses that occur in the area of disengaged frictionally engaging shift elements, certain frictionally engaging shift elements are replaced by form-locking shift elements. With automatic transmissions, which are implemented having both frictionally engaging shift elements as well as at least one form-locking shift element, and having a corresponding gear set design, at least one form-locking shift element must be engaged in the power flow of the transmission device to carry out a defined shift command.
Disadvantageously, depending on the design arrangement of the shift elements, while performing a request for a change of operating state of the transmission device, during which an engaged form-locking shift element is to be transferred into a disengaged operating state, the possibility exists that the form-locking shift element cannot be disengaged within an acceptable shift time with high shift comfort due to high drag torques which occur in the region of disengaged frictionally engaging shift elements, and/or due to a torque present during a downshift that is preferably without an interruption of tractive force.